The following background description constitutes a description of the background to the present invention, which does not, however, necessarily constitute prior art.
Vehicles, such as for example cars, buses and trucks are driven forward by an engine torque produced by an engine in the vehicle. This engine torque is provided to the driving wheels of the vehicle through a powertrain/driveline/drivetrain in the vehicle. The powertrain includes a number of components, such as e.g. a clutch, a gearbox/transmission device, shafts, and a differential. The powertrain may also include other components, and is described more in detail below.
In the gearbox/transmission, different gear ratios between an input shaft and an output shaft of the gearbox can be provided. Thus, the gearbox may change the gear ratio being provided by performing a gear shifting operation, e.g. including shifting a coupling sleeve between one or more of the gear wheels interacting in the gearbox, in order to provide a desired gear ratio for the gearbox.
A conventional gear shifting operation can be described as including four phases. The first phase of the gear shifting operation includes down-ramping of a powertrain torque Tpowertrain to 0 Nm, such that the gear initially used, which is often also called the current gear, can be disengaged after the first phase.
In the second phase of the gear shifting operation, the current gear is disengaged, i.e. a gear coupling sleeve is moved out of position, such that it does not anymore couple the gear wheel of the current gear to a main/transmission shaft in the gearbox. Then, the gearbox is synchronised with a target gear. i.e. the gear which should be used after the gear shifting operation is synchronised with a rotational target ωe_target speed of the main/transmission shaft. Then, the target gear is coupled/engaged/meshed with the main/transmission shaft in the gearbox, i.e. the gear coupling sleeve is moved/changed in to a new target gear position Gtarget, such that the target gear wheel is coupled/engaged/meshed with the main/transmission shaft in the gearbox in the new target gear position. In other words, a new target gear ratio between an input shaft and an output shaft of the gearbox is provided by shifting one or more gear coupling sleeves in the gearbox, such that a target gear position Gtarget for the gearbox is achieved. After the shifting, the target gear wheel is coupled/engaged/meshed with the main/transmission shaft in the gearbox, and the target gear ratio is provided by the gearbox.
In the third phase of the gear shifting operation, a play/backlash of the powertrain is eliminated/wound up. One or more of the components included in the powertrain may comprise a play/backlash, i.e. are coupled with a play/backlash. For example, different parts of a component, such as meshing gear wheels included e.g. in the gearbox and/or the differential, may have a play/backlash between them. In other words, the cogs/teeth of two interacting gear wheels of at least one powertrain component may at some time instances be out of contact with each other, such that no torque is transferred from the engine to the driving wheels, which is denoted play/backlash in this document. The play in the powertrain may cause oscillations in torque and/or revolutions, so called powertrain oscillations, in the vehicle when the vehicle, for example, starts moving once a torque has been requested from the engine. If the play/backlash is big/considerable, a difference Δω between a rotational speed ωshaft of an input shaft of a gearbox and a rotational speed ωwheel of a driving wheel of the vehicle will have time to also grow big/considerable before the play/backlash can be wound up by a torque applied on the input shaft. If the difference Δω is big/considerable when the play/backlash is gone/eliminated, the difference Δω results in big/considerable powertrain oscillations. Powertrain oscillations may cause vehicle speed variations, which make the vehicle rock longitudinally. These rocking movements in the vehicle are very disruptive for the driver of the vehicle.
Therefore, in some prior art solutions, strategies have been used at the request of engine torque in order to reduce these powertrain oscillations Such strategies utilise limiting torque ramps when the engine torque is requested. These torque ramps have been chosen in a way that the requested engine torque is limited such that the play/backlash is eliminated/wound up, and the powertrain oscillations are reduced. For example, the torque ramp should, according to some prior art solutions, initially be limited to being relatively flat in order not to apply too much energy into the powertrain per time unit, which would then result in powertrain oscillations.
In the fourth phase of the gear shifting operation, the engine torque is ramped up to the torque requested by the driver and/or driving assisting devices, such as vehicle speed/cruise control systems. In the fourth phase, the torque ramps used are usually steeper/less flat than in the third phase.